1. Field of the Invention
The present invention relates to sterilization systems and, more particularly, to vapor phase sterilization systems.
2. Description of the Prior Art
There is often a need to sterilize the interior of a container or a room due to some unexpected contamination or to prepare the container or room for a special use. For example, clean rooms are needed to manufacture certain kinds of microelectronic products and pharmaceuticals. The room must be periodically sterilized. The interior of incubators may require sterilization to rid them of pathogenic contaminants. In addition, laboratory spills of highly contagious substances may unexpectedly contaminate an area. Such containers and their contents are not easily sterilized by conventional methods.
Gaseous sterilization systems, such as ethylene oxide, formaldehyde, ozone and hydrogen peroxide, have bee used with varying success in a variety of applications. One problem with each of these sterilants is disposing of the residual vapors following sterilization. See DISINFECTION, STERILIZATION, AND PRESERVATION, 592, 677 (S.S. Block 2d ed. 1977).
Conventional gaseous/steam sterilization systems use vacuum pumps to evacuate chambers prior to introduction of the sterilant. Air blowers and injection pumps, or a vacuum source and gravity feed injection system are also commonly used in such sterilization systems. Due to the extreme pressure differentials required, vacuum or pressure systems require the use of sturdy, rigorously sealed vacuum/pressure vessels.
One arrangement for a steam-heated autoclave is disclosed by Linder U.S. Pat. No. 3,773,466, which issued on November 20, 1973. The system described by Linder includes an autoclave, a heating chamber for generating steam, a water tank and a steam trap. Steam entering the autoclave forces air out to the steam trap and to the water tank. At the end of the cycle, steam flows from the autoclave, back through the heating chamber through a three-way valve to the water tank. When pressure within the system is equalized, water flows by gravity from the water tank to the heating chamber for use in subsequent cycles. A related system is disclosed in Linder U.S. Pat. No. 3,443,884.
Moore et al. U.S. Pat. No. 4,169,123, and Forstrom et al. U.S. Pat. No. 4,169,124, both of which issued on Sept. 25, 1979, disclose methods of "cold" gas sterilization using hydrogen peroxide gas at temperatures below 80.degree. C. Moore recommends that liquid hydrogen peroxide should be volatilized within the sterilization chamber but indicates also that the volatilization may occur outside of the chamber. The hydrogen peroxide vapor may then be introduced into the sterilization chamber by air displacement. Moore provides no details as to how the introduction of the vapors by air displacement is to be achieved.
Bier U.S. Pat. No. 4,642,165, which issued on Feb. 10, 1987, discloses a method of vaporizing successive increments of a multicomponent liquid, such as an aqueous solution of hydrogen peroxide, for injection into a vacuum chamber. The vacuum in the chamber draws the multicomponent vapor into the chamber.
Koubek U.S. Pat. No. 4,512,951, which issued on Apr. 23, 1985, discloses a method of liquid-contact hydrogen peroxide sterilization. Goods to be sterilized are maintained in the sterilization chamber at a temperature below the dew point of the vapor sterilant. An aqueous solution of hydrogen peroxide is vaporized and passed into the evacuated sterilization chamber where, upon contact with the goods, the vapor condenses to form a liquid layer of sterilant on the goods. The vacuum in the chamber draws the vapor in.
United Kingdom Patent No. 1,582,060, issued to Tetra Pak International, discloses a similar liquid contact hydrogen peroxide sterilization method operated without a vacuum chamber. Liquid hydrogen peroxide is pumped to an ultrasonic spray nozzle which is operated by a stream of dehydrated air. A mist of hydrogen peroxide is sprayed into a container and mixed with hot air to change the mist into a vapor. The vapor is piped into a nonpressurized sterilization chamber where it condenses on a cool, moving web of material. A stream of hot air in an adjacent chamber removes the hydrogen peroxide layer from the web. The stream is then passed to a water separator where it is relieved of the sterilant.
United Kingdom Patent No. 1,574,488 also discloses a method for removing liquid hydrogen peroxide by means of a hot air stream.
Hydrogen peroxide, although irritating to the skin and eyes, decomposes to water and oxygen. A variety of materials are known which catalytically decompose hydrogen peroxide upon contact. Exotic metal catalysts, such as platinum black, have been evaluated as described in Gaglia, Jr. U.S. Pat. No. 3,912,451, issued on Oct. 14, 1975, for use in removing hydrogen peroxide from contact lenses.
The use of manganese dioxide (MnO.sub.2) supported on alumina in a continuous, tubular, packed bed reactor was evaluated for the catalytic decomposition of hydrogen peroxide by Kohler et al. "Catalytic Decomposition of Hydrogen Peroxide by ManganaseAlumina", NTIS Document PB 80-124274, National Science Foundation, Washington, DC (1974). The MnO.sub.2 does not completely destroy incoming hydrogen peroxide. A second treatment stage employing immobilized catalase is used to destroy any residual hydrogen peroxide.
Other materials which are known to catalyze hydrogen peroxide are metals, such as lead, iron, copper, cobalt, silver, gold and palladium. Houlsby U.S. Pat. No. 4,521,375 discloses the use of pyruvic acid and salts thereof to destroy hydrogen peroxide. It is also known that heat will lead to the decomposition of hydrogen peroxide.
There is a need for a simple, inexpensive system, preferably in modular form, for use with existing nonpressure or pressure containers or vessels, to generate a sterilant vapor, deliver it to the area to be sterilized and then dispose of the residual vapors.